Process of making pressure sensitive record material



S PA I' IZBVI OFF-I CE I PROCESS F MAKING PRESSURE SENSITIVE RECORD MATERIAL Barrett K. Green, Dayton, 01110,;35Sign0r topThe National Cash Register Company, Dayton,- Ohio,

.a corporation of Maryland N0 Drawing. ApplicationNovemberS, 1947, Serial No. 784,939

12 Claims.

This invention relates to improvements in process of making a pressure-sensitive record material. This application is a continuation in part of the pending applications of Barrett K.

coatings for recordmaterial, now abandoned, as a division of saidco -pending application Serial No. 581,834.

The principalobject of this invention is to ing: a-pressure-sensitive record material thatIis not subject to thesdefects anddisadvantages of that disclosed in Patent ,No.. 2,299,693, as indicated above.

Green, Serial No.'520,'573, filed January .31, 1944, 5 Another object of the present invention is to for Record material and coating for same, now provide vaprocess of making a record material abandoned; Serial No. 581,834, filed March 9, uponwhicha mark ,of,distinctive color may be 1945, for Coating for record material, now abanproduced, atthe points of application of localized 'doned; and SerialNo. 601,761,'filed June 2'7, 1945, pressure thereto, by such,,mere application of for Method of making pressure-sensitive marking localized pressure, and whichrwillnot become discolored ;orstained due ,tothe effect of light, atmospheric conditions, or aging.

In short, it is the;object ofthis invention to .provide a pr0cess of makings. pressure-sensitive provide a process of making a pressure-sensitive l5 record material in which the .markof distinctive record material, on. which a mark of distinctive color will be produced only at the points of applicolor may .be produced by the mereapplicationof cation of localized pressure, and at no other localizedpressuraand which is not subject to the points, andunder notother conditions. disadvantages inherent in the pressure-sensitive Another; object .of thisinvcntion is to provide record material disclosed in United States Leta process .of makingapressure-sensitive record ters Patent No. 2,299,693, patented OctoberQO, material in-whichthe mark of distinctive color is 1942, on the application filed by BarrettK. Green produced by the chemical reaction of color-formon February 23, .1940. That patent discloses a ing reactants, in the absence of any liquid ionizpressure-sensitive record material including the ing medium therefor.

combination of an insulating medium, :a rupturable solid material such as-gum dammar, having included therein interspersed droplets of aplurality of liquid reagents, which are chemically reactive to produce a distinctivecolor in the record materialatthe points of application of localized pressure thereto, such pressure rupturing the insulating medium to permit chemicalreaction between the two liquid reagents. The two reagents disclosed in :this patentare gallic acid and ferric ammonium sulphate, each dissolved in glycerine. These reagents are ionized by the glycerine, which constitutes an-ionizing medium, and the chemical reaction proceeds by interchange of ions when the twosolutions are allowed to mix, upon the rupture of the insulatin medi- 11111. The reaction disclosed in that patent depends upon the presence of-thereagents in .an ionizing medium. However, any available ionizing medium is hygroscopic, with the result that the record materiaL-made in accordance-with this patent, is sensitive to an excess of moisture, and conditions of high humidity may causethe insulating mediumto cease to be efiective, with the result that the chemical reaction takesplace without any application of, localized pressure, and the record material is stained and discolored, so that it ceases to be useful.

.As stated above, the. principal object of the present invention istosproVide a process ofmak- Av furtherobject of thisinvention is to provide aprocess ,ofxmaking a pressure-sensitive recordlmaterialflin which .a. mark .of-distinctive color is producedby a reaction betweensolid particles of color-forming reactants.

Further,objects,.and objects relating to details and economiesoi operation, will definitely appear from the detailed. description tofollow. The objects of this invention have been attained by the several embodiments thereof described in detail in the following specification. This invention is clearly defined and pointed out in the appended claims.

.In generahthe present invention contemplates a process of making a pressure-sensitive record material including ,the iforming on a supporting member a film-like deposit :of solid .partiEles :of a plurality of adsorption color-forming reactants disposed in contiguity witheach other, such reactants;beingvsogselected'thatsthey react, in the absence of a liquid ionizing medium forthe reactants, toiiorm a:distinctive:colcr whenbrought into adsorption contactzwith each other, and a solid insulating mediuminsulating saidreactants from color-forming reaction contact with each other. Upon application of localized pressure to the record materialgasby drawing a stylus across it, ,the insulating medium istruptured at the points ofzapplicationdofsaid localized pressure, and. such. rupture permits .coloreformmg reaction M contact between the reactants at such points, in the absence of any liquid ionizing medium for said reactants. The result is that a mark of distinctive color is produced by the mere application of localized pressure.

The color reaction employed is of the, so-called, adsorption type wherein an inorganic compound causes a color change in an organic compound coming into adsorption contact therewith.

Of the reactant materials employed the organic material is an electron donor aromatic compound having a double bond system which is convertible to a more highly polarized conjugated form upon taking part in an electron acceptor-donor solid surface chemical reaction, giving it a distinctive color, and the inorganic material is a material which is an acid relative to the organic material so as to be an electron acceptor when in adsorption contact therewith. Both materials are in fine particle form in order to furnish a large reactant surface area per unit area of the record material which enhances the depth of color per unit area of the record material.

According to one embodiment of the invention, solid particles of a plurality of color-forming reactants are interspersed in a solid insulating medium, which insulates the particles from colorforming reaction contact with each other. The rupture of this solid insulating medium by the application of localized pressure permits the solid particles of color-forming reactants to react with each other, at the points of application of such pressure, to produce the mark of distinctive color. According to another form of this invention, solid particles of one of the color-forming reactants are carried by and dispersed in a solid insulating medium, to which a coating of solid particles of another color-forming reactant is applied. In this case, the application of localized pressure ruptures the solid insulating medium, at the points of application of such pressure, and brings about color-forming reaction contact between the solid particles of color-forming reactants at such points, thus producing the mark of distinctive color. Preferably, this pressuresensitive record material includes a base web, such as a fibrous Web of paper or the like, to which the coating of solid insulating medium and the color-forming reactants is applied.

The insulating medium is a pressure-rupturable film derived from an organic film-forming, hydrophilic col oid substance.

Since it is difficult to show precisely the spatial relationship between the solid particles of colorforming reactants, the solid insulating medium, and the base web, it is preferred not to attempt to illustrate any embodiment of this invention by drawings.

In the following examples, there will be described embodiments of this invention, by means of which the objects of the invention have been successfully attained.

The following embodiment of this invention constitutes the best mode of applying the prinoiple thereof contemplated up to the present time, and may be considered the preferred embodiment. It consists in a process for making a pressure-sensitive record material that comprises a base web, of paper or the like, to which is applied a coating including casein and solid particles of three color-forming reactants; namely, kaolin, the compound 3,3 bis (p-climethylaminophenyl) -6 dimethylamino phthalide,

a referred to as crystal violet lactone and hav ing the structure and the compound tetramethylbenzidine, having the structure The casein constitutes the solid insulating medium, insulating one of the color-forming reactants-that is, kaolin-from color-forming reaction contact with the other color forming reactants-that is, crystal violet lactone and tetramethylbenzidine. This record material is normally white or bluish white in color, and, upon the application of localized pressure thereto, as by drawing a stylus thereover, a dark blue mark is produced at the points of application of such localized pressure. Such application of pressure ruptures the solid insulating medium at the points of application of pressure, permitting color-forming reaction contact between the solid particles of kaolin and the solid particles of crystal violet lactone and tetramethylbenzidine, thus causing the color change at such points that produces the mark.

The compound 3,3 bis (p-dimethylaminophenyl) -6 dimethylamino phthalidethat is, crystal violet lactone-and the process of making it are disclosed in United States Letters Patent No. 2,417,897, issued March 25, 1947, on the application of Clyde S. Adams filed June 16, 1945, although the compound is incorrectly named in said patent as 3,3 bis (4-di1nethylaminophenyl)-6 dimethylaminophenyl phthalide. Reissue Patent Re. 23,024 correctly names the compound.

It is not considered that the proportions, in Which these several ingredients are present in the record material, are of particular importance, but good results have been obtained with a pressure-sensitive record material having such ingredients present in the following proportions by weight in the coating on the base web:

Per cent Casein 8.85 Kaolin 88.50 Crystal violet lactone 2.25 Tetramethylbenzidine .40

When these ingredients are applied to the paper as a coating thereon, such coating weighs about .0023 pound per square foot or" surface and may have a thickness of the order of from .0005 to .001 inch. The thickness of the coating varies, of course, with the treatment to which the record material is subjected in finishing. The solid particles of kaolin in this record material may be of about the order of ten microns in diameter, although considerable variation in par ticle size is possible without any ill elfects. Particle size of the crystal violet lactone and the tetramethylbenzidine is largely determined by the method of application of those ingredients. The

ascent-i w particles of these reactants may be as large as ten microns in diameter and frequently are much smaller.

Gelatin, methyl cellulose, starch, polyvinyl alcohol, and animal glue are representative organic hydrophilic colloid materials that may be substituted for casein as the solid insulating me: dium. Any of the following inorganic materials may be substituted for kaolin as one of the colorforming reactants: attapulgite (Attapulgus clay), pyrophyllite, talc, bentonite, halloysite, calcium sulphate, calcium citrate, magnesium trisilicate, zinc sulphide, Zirconium dioxide, calcium phosphate, barium sulphate, and calcium fluoride. When any of these materials are substituted for the kaolin in this combination, the resulting record material will be white or bluish white in color, and a dark blue mark will appear thereon as the result of the application of localized pres.

sure.

If the tetrainethylbenzidine be omitted and the pressure-sensitive record material be made using kaolin and crystal violet lactone as the sole color-forming ingredients, the record material will be white in color, and application of localized pressure will produce a dark blue mark thereon, out this mark may fade upon continued exposure to light under conditions of high hu. midity. On the other hand, if the crystal violet lactone be omitted and tetramethylbenzidine and kaolin be used as the sole color-forming reactants, the pressure-sensitive record material pro.- duced will be normally white, and application of localized pressure thereto will produce a green mark, which deepens in color upon aging and does not fade as readily as the mark produced by crystal violet lactone and kaolin alone, under conditions of high humidity.

This pressure-sensitive record material is not substantially affected by the amount of atmospheric humidity ordinarily encountered, although the mark may fade somewhat if subjected to high humidity for a long-continued period of time. However, this pressure-sensitive record material does not become stained or discolored by exposure to high humidity for-long periods or time, and retains its ability to respond to the application of localized pressure, and to produce the mark of distinctive color, under such conditions. Ehis is thought tobe due to the fact that the record material does not include any hygroscopic ionizing media. Consequently, the structure of the record material is not altered or modified due to the absorption of water from the atmosphere.

A method constituting one embodiment of this invention that has been used successfully to make the pressure-sensitive record material described above is as follows: A slurry of kaolin and water was prepared including fifty parts by weight of lin throughout the slurry. The addition of this dispersing agent reduces the viscosity of the slurry considerably, thus facilitating its mixing and application, and also preventing the settling of the solid particles of kaolin. A 20% by weight solution of casein in water was formed by, first, dispersing the casein in cold water by stirring ior fifteen minutes atroom temperature and, then, heating upto degrees centigrade, Five parts by weight, of a 28% ammonium hydroxide, solue h tion-that is, one having a specific gravity of 25.9 31%., at

we e hen ad ed to he n cas in s l i which was stirred for about fifteen minutes and allowed to cool to room temperature. The kaolin slurry and. the alkalin ca ein o ti n e ii n' eughly mixed and blended, in' the ratio ten parts b Wri ht 9i kao i to o c o i i n at this stage, a small percentage ior instance, abgut. 0.05% by weight-of a -solution of equal parts by weight of tributyl phosphate in alcohol. er ethe aai feem 'r e a t' e d d-i his n ture of the res n slurryandthe c'as-ein'so int n was then applied as a coating to the paper, an the coated paper was dried and calendere'd 9r treated inany desiredway to give the proper surface finish. A solution in toluene of about 255% by weight of crystal'violet lactone and about .45%. by weight oftetramethylbenzidine was then applied to the coated side of thepaper, the excess of this solution was removed in an3' suitable way, as by passing under a doctor blade, and then the treated paper was dried to evaporate the toluene, and was ready for use.

Another embodiment of this invention success fully used for making pressureesensitive record material such as described above, using casein asithe solidinsulating medium and kaolin, crystal violet last-one, and tetrainethylbenzidine as the color-forming reactants, is as follows: 206 grams o'fkaolin were'made into a slurry with 200 grams of water, to which 6.3% byflweight of sodium nietaphosphate was added as a dispersing agent. A casein'solution was formed by dispersing 20 grams 10f casein ,in 139 grams of cold water and stirring for fifteen minutes. This dispersion of casein in water wasthen heated to 60 degrees centigrade, and 5 grams of commercial 28% ammonium hydroxide solution were added and the solution stirred for fifteen minutes while hot, after which it was allowed to cool to room tem perature. One-half of the casein solution thus formed was thoroughly mixed with the kaolin slurry. 5.1 grams of crystal violet lactone and .9 gram of tetramethylbenzidine were then dissolved in 50 cc. of 3.7% hydrochloric acid solution, having aspecific gravity of 25 B. at

centigrade hour. The portion of the casein solution containing the kaolin was passed through a homogenizer, or other means for mixing and thoroughly dispersing the particles of kaolin in the casein solution, and the two portions of casein solution, one containing the kaolin and the other containing the crystal violet lactone and the tetramethylbenzidine, were then mixed thoroughly and applied as a coating to the base web or paper. This coating-was then dried on the paper in the usual manner. The resulting record material had a light bluish-white color approaching White.

It should be noted that the mixing of tha amrnoniacal.kaolin-containing portion of the casein solutionwith the other portion of the casein solo;

.75 tion, containing the crystal violet lactone and the tetramethylbenz idine, results in an alkaline mixture, in which the crystal violet lactone and the tetramethylbenzidine are precipitated in extremely fine particles.

In case gelatin is substituted for casein as the solid insulating medium, the procedure described above is modified, in that the gelatin is first dissolved in water at a temperature above 40 degrees centigrade, and this gelatin solution is then divided into two equal parts, to one of which the slurry of kaolin and water is added as before. The other part of the gelatin solution is made sufficiently ammoniacal to neutralize and precipitate the crystal violet lactone and the tetramethylbenzidine when the hydrochloric acid solution of these ingredients is added thereto. These two portions of the gelatin solution are then mixed, and the mixture is applied as a coating to the paper and then dried. It should be noted that, when the gelatin is used as the solid insulating medium, the gelatin solution should be kept at a temperature above 40 degrees centigrade throughout the entire procedure.

In case methyl cellulose is used as the solid insulating medium in substitution for the casein, a solution is prepared by dissolving about parts by weight of methyl cellulose (of any vscosity between 2000 and 4000 centipoises at 68 degrees Fahrenheit) in about 50 parts by weight of water, and this solution is divided into two equal parts. To one portion of the methyl cellulose solution, the slurry of kaolin and water is added, in the ratio of 40 parts by weight of kaolin to one part by weight of methyl cellulose, and mixed, as described in connection with the use of casein. The other portion of the methyl cellulose solution is rendered sufficiently ammoniacal to precipitate the crystal violet lactone and the tetramethylvbenzidine from the hydrochloric acid solution thereof, when the latter is added to and mixed with this portion of the methyl cellulose solution in such proportions that the ratio by Weight of ,kaolin to crystal violet lactone and tetramethylbenzidine in the coating will be 100 to 3. The two portions of the methyl cellulose solution are,

then, thoroughly mixed and applied as a coating to the paper, which coating is dried.

Another embodiment of this invention produces a material comprising a base web of paper or the like having applied thereto a coating including casein or methyl cellulose as the solid insulating medium and solid particles of two color-forming reactants; namely, kaolin and the compound 3,3 bis (p-dimethylaminophenyl) phthalide, also known as malachite green lactone, having the structure This record material is normally white or light in color, and, upon application of localized pressure thereto, as by drawing a stylus thereover, a mark of dark blue-green color is produced at the points of application of such pressure. The process for making the novel record material with malachite green lactone is claimed in a divisional application Serial No. 63,211, filed December 2, 1948.

Another embodiment of this invention pro duces a material that comprises a base web of paper having applied thereto a coating including casein as the solid insulating medium and two color-forming reactants; namely, kaolin and the compound 2,4-bis [p-(p-dimethylaminophenylazo) anilinol G-hydroxy sym. triazine, having the structure The pressure-sensitive record material made using these ingredients is normally yellow in color, and the application of localized pressure thereto, as by drawing a stylus across the material, ruptures the solid insulating medium and permits the solid particles of kaolin and the organic color-forming reactant to come into color-forming reaction contact with each other, producing a dark blue mark at the points of application of such localized pressure.

The process of making record material with the above triazine compound is disclosed in divisional application Serial No. 63,212, filed Deceme her 2, 1948.

Another embodiment of this invention produces a pressure-sensitive record material including a base web of paper having applied thereto a coating including casein as the solid insulating medium and two color-forming reactants; namely, kaolin and the compound o-hydroxybenzalacetophenone, having the structure This record material comprises solid particles of kaolin and o-hydroxybenzalacetophenone insulated from color-forming reaction contact with each other by casein as the solid insulating medium. The record material is normally light yellow in color, and application of localized pressure thereto ruptures the insulating medium at the points of application of such pressure, permitting color-forming reaction contact between the particles at such points and producing a reddishyellow mark.

The process of making record material with o-hydroxybenzalacetophenone is claimed in a divisional application Serial No. 63,213, filed December 2, 1948.

Another embodiment of this invention produces a pressure-sensitive record material consisting of a web of paper having applied thereto a coating comprising casein as the solid insulat-- ing medium and two color-forming reactants; namely, kaolin and the compound bis (p-dimethylaminophenyl) methanol, also known as Mich! lers hydrol and having the structure In this record material, the casein forms the abuser;

insulating medium at the points of application of such pressure, permitting color-forming reaction contact between the particles, producing dark .blue mark. The record material is normally white or light gray in color.

The process of making record material with Michlers hydrol is claimed in a divisional application, Serial No. 63,214, filed December 2, 1948, which also claims record material made with the methyl ether of Michlers hydrol as described in the next paragraph.

Another embodiment of this invention produces a record material consisting of a web of paper having applied thereto a coating comprising casein as the solid insulating medium and two color-forming reactants; namely, kaolin and the compound bis (p-dimethylaminophenyl) ,methoxymethane, also known as (methyl ether of Michlers hydrol, having the structural formula According to this embodiment, the casein constitutes the solid medium insulating thesolid .particles of kaolin and bi methyl ether of .Michlerfs hydrol from color-forming reaction contact with each other, and, when this solid insulating ,medium is ruptured by the application of localized pressure, color-formingreaction contact between the particles .is ,permittedlat the points ,of application of such pressure, producing a .dark blue Thecasein'constitutes the solid insulatingme- ,dium, which insulates the solidlparticles of kaolin :from color-forming reaction contact with the .solid particles of 3,3 bis (p-diethylaminophenyl) phthalide. The material is normally whitabut application of localized pressure thereto, as vby drawing a styluszacross it, IEZOdllGGSgS, blue-green mark at the points of1 application of suchpr s ur duets the localized rupture of the insulatingme- -dium, permitting color-forming reaction contact between thereactant particles: at such points.

The process of :making record material with 3,3 bis lp-diethylaminophenyl) ,phthalide is "claimed in a divisional application ,Serial No. 63,215, filed December 2, 1948, which. application -also claims .theprocess of makingrccordmaterial with the compound-3,3 .bis lp-di-n-propylaminophenyl) phthalidedescribed inasubsesuent paragraph.

, Another embodiment .oithis inventionproduces ea pressureesensitive recordmateitial comprisinea web of paper hav ng apphed thereto a coating in- CHsHN- NHO H3 This record material is normally white, but the a plication of localized pressure thereto ruptures the insulating medium, casein, at the points of application of such pressure, permitting coloriorming reaction contact between the solid particles of kaolin and the solid particles of the compound 3,3 bis (p-methylaminophenyl) ,phthalide, resulting in the production of a bright blue mark.

The process of making record material with the above phthalide and that made with the phthalide compound described in the next paragraph is claimed in a divisional application, Serial N0. 63,216, filed December 2, 1948.

Another embodimentlof this invention produces a pressure-sensitive record material consisting of a web of paper having applied thereto a coating consisting of casein as the solid insulating medium and solid particles of two color-forming reactants; namely, ikaolin and the compound 3,3 bis (p-ethylaminophenyl) phthalide, having the structural formula This record materialis normally white, butthe application of localized pressure thereto ruptures the vsolid insulating medium at thepoints of application of such pressure, thus permitting colordimethylaminobenzohydr-yl) 5 dimethylamino benzoic acid, having the structural formula In this embodiment, also, thecasein constitutes divisional application,

the solid insulating medium, insulating the solid particles of kaolin and the compound 201,4 bis dimethylaminobenzohydryl) dimethylamino benzoic acid from color-forming reaction contact with each other. The record material is normally white, and the application of localized pressure thereto ruptures the solidinsulating medium at the points of application of such pressure, permitting color-forming reaction contact between the solid particles of the reactants, producing a dark blue mark.

The process of making record material with the above benzoic acid compound is described in a divisional application, Serial No. 63,217, filed December 2, 1948.

Another embodiment of this invention produces a record material consisting of a web of paper having applied thereto a coating including casein as the solid insulating medium and solid particles of two color-forming reactants; namely, kaolin and the compound 3,3 bis (p-di n-propylaminophenyl) phthalide, having the structural formula sure to this record material ruptures the insulating medium. and permits color-forming reaction contact between the solid particles of the two reactants, thus producing a blue-green mark at the points of application of such pressure.

Another embodiment of this invention rproi duces a record material consisting of a web of paper having applied thereto a coating including casein as the solid insulating medium and solid particles of two color-forming reactantskaolin and the compound 3,3 bis (4-dimethylamino 3-methyl-phenyl) phthalide, having the structural formula CH; CH: 7

(CHs)sN 01 1 This record material is normally white, but a blue mark is produced thereon by the application of localized pressure, which ruptures the insulating medium, casein, and permits color-forming reaction contact between the solid particles of the reactants at the points of application of such localized pressure.

The process of making record material with the above phthalide compound is claimed in a Serial No. 63,218, filed December 2, 1948.

Another embodiment of this invention produces a record material consisting oi. a web of paper having applied thereto a coating including casein as the solid insulating medium and solid particles of two color-forming reactants; namely, kaolin and the compound 4.-- (p-dimethylaminophenylazo) benzanilide, having the structural formula 0 tact between the solid particles of the reactants and thus producing the distinctive mark.

The process of making record material with the benzanilide compound is claimed in a divisional application, Serial No. 63,219, filed December 2, 1948.

The pressure-sensitive record materials disclosed herein are not claimed in this application but are disclosed and claimed in the pending a plication of Barrett K. Green, Serial No. 784.938, filed November 8, 1947, for Pressure-sensitive record material.

It is understood that the process of making a pressure-sensitive record material described herein is susceptible of considerable variation :vithout departing from the spirit of the inven ion.

What is claimed is:

1. The process of making a pressure-sensitive record material inc uding the forming on a supporting member a film-like deposit of solid particles of a plurality of adsor tion color-forming reactants disposed in conti uity with each other and a solid insulating medium. derived from an organic film-forming hydronhilic colloid substance, insulating said reactant p rticles from color-forming reaction with each other, at least one of said reactants being an inorganic compound and at least another of said reactants being an organic compound adsorbable with it, said reactants being so selected as to react. in the absence of a liquid ionizing medium for the reactants, to form a distinctive color when brought into contact with each other the organic reactant being an electron donor aromatic organic compound having a double bond system which is convertible to a more highly polarized conjugated form upon taking part in an electron acceptordonor solid surface chemical reaction, giving it a distinctive color, and the inorganic reactant being in fine particle form providing a large adsorbent surface area and which is an acid relative to the organic reactant so as to be an electron acceptor when in adsorption contact with said organic reactant.

2. The process of claim 1 in which the solid insulating medium is casein.

3. The process of claim 1 in which one of the color-forming reactants is kaolin.

4. The process of claim 1 in which the organic color-forming reactant is the compound 3,3 bis (p dimethylaminophenyl) 6 dimethylamino phthalide, having the structure (CH3)2N' N(CHa)z l O-$=O N (0113):

and another of the color-forming reactants is tetramethylbenzidine, having the structure wasnwOQ-monm 5. The process of claim 1 in which the organic color-forming reactant is the compound 3,3 bis (p-dimethylaminophenyl)-6 dimethylamino phthalide, having the structure 6. The process of making a pressure-sensitive record material including the steps of forming on a supporting member a film of solid insulating material having particles of a first colorforming inorganic reactant dispersed therein, and depositing on said film particles of a second organic color-forming reactant adsorbable on the first reactant particles, said reactants being so selected as to form a distinctive color when brought into adsorption contact with each other,

and said solid insulating material being derived from an organic film-forming hydrophilic colloid substance such as to insulate the reactants from color-forming reaction contact with each other the organic reactant being an electron donor aromatic organic compound having a double bond system which is convertible to a more highly polarized conjugated form upon taking part in an electron acceptor-donor solid surface chemical reaction, giving it a distinctive color, and the inorganic reactant being in fine particle form providing a large adsorbent surface area and which is an acid relative to the organic reactant so as to be an electron acceptor when in adsorption contact with said organic reactant.

7. The process of claim 6 in which the film of solid insulating material is formed by evaporating the solvent from a solution of the solid insulating material having particles of the first coloriorming reactant dispersed therein.

8. The process of claim '7 in which the layer of particles of a second color-forming reactant is deposited on said film by coating the film with a solution of said reactant and evaporating the solvent therefrom.

9. The process of claim 6 in which the solid insulating material is casein.

10. The process of claim 6 in which the first color-forming reactant is kaolin.

11. The process of claim 6 in which the second color-forming reactant is a mixture of the compound 3,3 bis (p-dimethylaminophenyl) -6 dimethylamino phthalide, having the structure and the compound tetramethylbenzidine, having the structure 12. The process of claim 6 in which the second color-forming reactant is the compound 3,3 bis (p-dimethylaminophenyD-6 dimethylamino phthalide, having the structure I Ha)2 BARRETT K. GREEN.

REFERENCES CITED The following references are of record in the OTHER REFERENCES Hauser et al.: Journal Amer. Chem. Society, vol. 62, July 1940, pages 1811 to 1814. 

1. THE PROCESS OF MAKING A PRESSURE-SENSITIVE RECORD MATERIAL INCLUDING THE FORMING ON A SUPPORTING MEMBER A FILM-LIKE DEPOSIT OF SOLID PARTICLES OF A PLURALITY OF ADSORPTION COLOR-FORMING REACTANTS DISPOSED IN CONTIGUITY WITH EACH OTHER AND A SOLID INSULATING MEDIUM, DERIVED FROM AN ORGANIC FILM-FORMING HYDROPHILIC COLLOID SUBSTANCE, INSULATING SAID REACTANT PARTICLES FROM COLOR-FORMING REACTION WITH EACH OTHER, AT LEAST ONE OF SAID REACTANTS BEING AN INORGANIC COMPOUND AND AT LEAST ANOTHER OF SAID REACTANTS BEING AN ORGANIC COMPOUND ADSORBABLE WITH IT, SAID REACTANTS BEING SO SELECTED AS TO REACT, IN THE ABSENCE OF A LIQUID IONIZING MEDIUM FOR THE REACTANTS, TO FORM A DISTINCTIVE COLOR WHEN BROUGHT INTO CONTACT WITH EACH OTHER THE ORGANIC REACTANT BEING AN ELECTRON DONOR AROMATIC ORGANIC COMPOUND HAVING A DOUBLE BOND SYSTEM WHICH IS CONVERTIBLE TO A MORE POLARIZED CONJUGATED FORM UPON TAKING PART IN AN ELECTRON ACCEPTORDONOR SOLID SURFACE CHEMICAL REACTION, GIVING IT A DISTINCTIVE COLOR, AND THE INORGANIC REACTANT BEING IN FINE PARTICLE FORM PROVIDING A LARGE ADSORBENT SURFACE AREA AND WHICH IS AN ACID RELATIVE TO THE ORGANIC REACTANT SO AS TO BE AN ELECTRON ACCEPTOR WHEN IN ADSORPTION CONTACT WITH SAID ORGANIC REACTANT. 